The use of heat-shrinkable thermoplastic films in many packaging applications is well known. Usually a product is enclosed in a film, sealed, and then heat is applied thus shrinking the film snugly about the product. One of the most useful and satisfactory thermoplastic materials for packaging film is polyethylene. In the prior art, there are a number of methods to convert raw polyethylene into a suitable, heat-shrinkable packaging film. One such method is disclosed in U.S. Pat. No. 2,855,517 issued to W. C. Rainer et al. on Oct. 7, 1958. Another method is taught by U.S. Pat. No. 3,022,543 issued to W. G. Baird, Jr. et al. on Feb. 27, 1962. In the Baird method, polyethylene is continuously extruded in the form of a tube, drawn, irradiated with electrons to crosslink the molecules, heated, and stretched again by applying internal pressure to the tubing. The resulting film usually has good heat shrinking properties but relatively low tear strength. Once a tear has begun it tends to rapidly propagate during the heat shrinking process resulting in destruction of the film. One method of overcoming this low tear strength is disclosed in U.S. Pat. No. 3,754,063 issued to Henry G. Schirmer on Aug. 21, 1973. In the Schirmer patent, a method of extrusion coating crosslinked polyethylene with a layer comprising a mixture of isotactic polypropylene, polybutene-1, and atactic polypropylene to improve the tear strength, bursting resistance, and heat sealing proprties of polyethylene is taught. However, while packaging materials, particularly bags for food products, made from the coated polyethylene material disclosed in the Schirmer patent are generally quite satisfactory, it was discovered that it was necessary to dust bags and films made from such coated polyethylene with cornstarch in order to prevent them from sticking together during storage. This dusting proved to be a time consuming production step and the dust, while not harmful, is an annoyance in handling the bags. Thus, it is an object of the present invention to provide a superior packaging material which does not require excessive dusting.
Another object of the present invention is to provide a coated polyethylene film product having improved abuse resistance and orientation properties with a reduced stickiness or tackiness.
Still another object is to provide a film which is easier to handle, stack, and use when made into pouches and bags.
The accomplishment of these and other objects will become obvious from the description of the present invention which follows.